Genetic science is racing ahead toward a day when doctors will be able to predict what diseases you’re susceptible to. But do you really want to know?

Doctors can now take a few of your cells, pull out the DNA, stretch it across a screen and diagnose more than 1,100 genetic defects that could mean trouble, ranging from rare disorders to more common ones like heart disease and cancer.

Surprising even the experts, genetic testing is racing ahead faster than doctors, genetic counselors and others can keep pace, driven by scientists eager to claim the prize of predicting diseases before they happen and perhaps preventing them.

The potential of the field raises questions for a public wary of peering into the genetic future and jaded by unfulfilled medical promises. How will people handle the news that ticking away in every cell of their body are potential disease genes inherited from their parents, which they in turn may have passed on to their children?

And everybody has them. Geneticists estimate that each person may have more than 30 genes that make them susceptible to a variety of disorders. A person’s risk of developing a specific disease depends on which genetic combination he or she possesses in conjunction with environmental stressors arising from lifestyle choices or chemical exposure.

“Knowledge is a good thing when you can use it productively,” said Dr. Wylie Burke, chief of medical history and ethics at the University of Washington. “But sometimes it’s not a good thing. This whole genetic risk era is going to push us to think very carefully about that.”

Many people are especially concerned about genetic discrimination–using abnormal genes to deny jobs or health insurance–and tests for genes that cause deadly illnesses for which there currently is no treatment, such as Huntington’s disease.

A test for the Huntington’s gene has been available for a decade, but it has been shunned by people at risk–children of parents with the disease–who don’t want to live for years knowing the illness will start destroying their brain in midlife. And although an eight-year-old test can identify a gene associated with Alzheimer’s disease, few physicians offer it to patients out of fear they might become despondent.

Still, some recent studies suggest people might be more willing to take the news in stride and act on it, especially if they are told the difference between a gene that causes a disease 100 percent of the time–as with Huntington’s–and a gene that only increases their susceptibility, which is far more common.

Children of Alzheimer’s patients whose genes were tested overwhelmingly accepted the genetic findings without becoming depressed or anxious, Dr. Robert C. Green of the Boston University School of Medicine reported last week at an Alzheimer’s conference in Washington, D.C.

Acting on genetic data

Those with the faulty gene also took steps to reduce their risk of contracting the disease, including exercising more, eating better, taking vitamins and engaging in mentally stimulating tasks, he said. “We found that learning you had a genetic risk marker made this more real to people and made them want to act on it,” Green said.

Genetic testing was once mostly limited to newborns and people with single-gene disorders like Huntington’s, but with the discovery in 1994 of two breast cancer genes, BRCA 1 and 2, the field rapidly expanded into the common adult killer diseases.

Between 1993 and 2004, gene tests jumped more than eleven-fold to 1,148, and the number of laboratories offering genetic testing increased more than fivefold to 577, according to the University of Washington’s GeneTests Laboratory Directory, a federally supported agency that lists available genetic tests.

Genetic testing costs anywhere from a few hundred dollars to thousands per test. Many health insurance companies pay for them, depending on the type of coverage.

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